Image point transform method for VSP data in VTI medium

Image point (IP) transform method is a very useful tool for VSP data processing and signal enhancement, wavefield separation and imaging because reflection events are mapped onto points by IP transform, and thus, they can be easily identified and separated from other events like direct waves and noise in IP domain. However, in practice, applying IP transform directly to seismic data for anisotropic media leads to misinterpretation because the propagation velocity varies depending on propagation angle in anisotropic media. In order to overcome this problem, we proposed an anisotropic IP transform method for vertical transversely isotropic (VTI) medium by calculating traveltime of incident and reflected wave path separately. During the calculation of traveltime for segmented ray path, the geometrical information of reflection points can be derived analytically. This information for reflection point can be directly used for the purpose of reflector imaging. In determining ray velocities of both waves, we applied bisection method to determine phase angle for a given propagation angle without any weak anisotropy approximation. We applied and validated anisotropic IP transform to numerical VSP data for dipping reflector model and reconstructed the reflectors' image using the information for reflection point that are determined during anisotropic IP transform.

Research Highlights
► We derive IP transform on VTI medium.
► We adopt bisection method to determine a phase angle.
► We show properties of anisotropic IP transform with numerical data.